Dispenser pumps, which dispense as a result of manual actuation of a part of the pump (and which are to be distinguished from valves which merely release pressurized contents such as an aerosol) from a container to which they are fitted, are conventionally made with a piston working inside a cylinder so that relative displacement of the piston in the cylinder either on an inward stroke or a release stroke will cause the discharge of material in a more or less accurately measured amount.
These pumps are comparatively cheap and in many cases disposable assemblies and the fewer number of parts they can be made of, the better. Particularly this is true in relation to parts such as pistons and cylinders which are necessarily separate and which undergo relative sliding movement.
In the present invention we avoid the use of a piston and cylinder, relying instead on a specially designed flexible wall of a pump chamber of the dispenser to cause the necessary volume change of that chamber when the pump is actuated.
This as such is not new. U.S. Pat. No. 3 029 742 (Curtis) for example describes a pump that has a deformable conical diaphragm with edge flaps acting as valve elements, using a separate spring assembly to restore the diaphragm to its expanded rest position after each stroke. U.S. Pat. No. 3 452 905 (Leeds & Micallef) shows a pump with a chamber partly defined by a dome-shaped flexible portion, which likewise relies on a spring for restoration. There are however problems with these flexible wall dispensers which so far have not been solved. Amongst these is the problem of conserving the maximum chamber volume through which there is displacement within the confines of the necessarily limited diameter of these objects; another is procuring the necessary restoration forces within the flexible wall to cause it to return to its rest position after each actuation without the need for a separate restoring spring. As mentioned above, the fewer the parts constituting the pump, the better. All these aims should therefore preferably be carried out while permitting the flexible wall to be made of the same material as forms other portions of the pump, since otherwise the flexible wall would have to be a special moulding, separately assembled with the dispenser.
A further problem concerns possible leakage into or out of a container fitted with such a dispenser pump when it is being sent out from the factory. The container may be laid on its side, inverted and shaken during its transport, but during this time must not leak contents. Nevertheless, provision must be made when the dispenser is in its working condition not only for the material to be dispensed freely through a discharge nozzle, but also preferably for displacement air to be vented back into the container through the pump.